This application relates to a speed gearbox for driving an auxiliary turbine engine component. More particularly, the application relates to a multi-speed gearbox driven by a turbine engine spool to drive an electrical generator, for example.
An increasing number of airplanes require significant electric power for operation. Typically, a generator is driven by a high pressure spool through a power takeoff shaft. Due to modern airplane engine efficiency requirements, the electric power demand is increasing beyond the power extraction potential of the engine high pressure spool. That is, the efficiency provided by the high pressure spool drops to an unacceptable level if the generator is to be driven to provide a needed amount of electric power.
Power extraction is available from the low pressure spool of the engine, but the speed range is significantly higher than the high pressure spool (for example, approximately 5:1 for the low pressure spool and 2.22:1 for the high pressure spool). As a result, generators must be specially designed for use with the faster low spool to achieve the desired electrical output from a low spool-driven generator. Airplane and engine manufacturers are looking for ways to extract electric power and other accessory power from the low pressure spool in a cost effective and efficient manner.